In the past, providing advanced communications features to large companies with facilities at different locations required interconnection of a number of privately owned exchanges. U.S. Pat. No. 4,802,199 issued Jan. 31, 1989, to Michael D. Lange et al., for example, discloses a multiple exchange system aimed at the needs of large customers having facilities at a number of differrent geographic locations. The system provides repertory dialing through the switched network to set up connections between the different PBX's to emulate a dedicated private line connection. The system supports speed or repertory dialing, SMDR reporting and automatic routing features. The requisite processing capability for setting up the virtual private line connections between exchanges and providing special service features is located in the individual private exchanges. The problem with this approach is that the company must own, operate and maintain some form of private exchange at each of its locations. Also, in the Lange et al. system, the exchanges are PBX's interconnected via public or private switched network lines, and the company incurs the expense of these lines as well.
Rather than providing business services through a private exchange, such as a PBX, Centrex takes a group of normal telephone lines and provides call processing to add business features to the otherwise standard telephone lines. For example, the Centrex exchange adds intercom capabilities to the lines of a specified business group so that a business customer can dial other stations within the same group using extension numbers, such as a two, three or four digit numbers, instead of the full telephone number associated with each called line or station. Other examples of Centrex service features include call transfer between users at different stations of the business group, a number of varieties of call forwarding and speed calling. Thus, Centrex is a package of features that are placed or added onto the standard service provided via telephone lines that allow a group of lines assigned to a business customer to operate as a business system. Centrex typically provides business services similar to those provided by a PBX or PABX through a central office exchange of the public telephone network but without requiring the customer to purchase and maintain a private exchange.
Problems with the existing Centrex arise from the fact that Centrex features are provided individually by local switching offices. Consider switch based Centrex call transfer as one example. In the existing service, a business customer receives a call on one line but decides the caller should talk to an employee on another line. The currently connected individual could flash the switch hook and dial the second employee's extension number and hang up. The call is transferred by the central office over to the line of the second employee. If provided by a prior art Centrex, the transfer is confined to one central office. Consequently, the transfer feature works only so long as all of the employees of the particular business customer are served by the same central office. With such a service, a call cannot be transferred to a line connected to a remote office.
One way the problem of multiple locations has been addressed in the past is for the customer to purchase private tie line trunk circuits to connect remote facilities to the customer's exchange. In effect, when a remote employee wanted to call through the network to another employee, the remote employee took the station set off-hook and the set connected through a tie line to the distant exchange which provides the customer with the Centrex service. The calling employee then received the dial tone of the distant exchange via the tie line. Using digital switches, to achieve a similar result requires deployment of a remote switching module at the remote locations to supply foreign dial tone and connect the remote switching modules to the distant exchange via a fiber optic trunk. Every prior art system for extending Centrex type services to distant customer facilities therefore involves some form of private line to the remote locations. Use of any such private lines incurs mileage charges for the wires strung from the exchange to each distant extension.
Another problem relating to existing business services is illustrated by call routing. This type of service for outgoing calls selects one of three different line or trunk groups to place a call through. For a call from one city going to a distant city there might be a choice of going first via a Tie line, second to MCI and then to some kind of AT&T WATS line. Typically, a customer uses such call routing to control communication costs. The selection is made on a priority basis established by the customer in whatever manner produces the most economical use of their facilities. In the existing network, however, such call routing is controlled at the central office level of the network. The route selection priority for each Centrex line is programmed in the central office to which the line connects, and changing the priority for any given line requires a technician to go out to the central office switch and change the wiring and/or programming of that particular switch. Thus, if a business customer has multiple geographic locations connected to different central offices, if the customer desires to change the call routing priority for all locations, technicians would have to modify wiring and/or install another program table in each central office to which that customer's telephone lines connect.
Where the customer has a large number of lines to stations dispersed over a variety of geographic locations, typically a number of lines connect to one local central office and other lines connect to one or more remotely located central offices. In such a situation, some services, such as the call transfer discussed above, cannot be provided for all lines. Also, those services that can be provided require extensive programming and/or wiring at each connected central office switch to establish or change the service parameters as was discussed above with regard to call routing. Thus clearly a need exists for providing business type features to customers with facilities at a number of geographically diverse locations through the public telephone network.
In recent years, a number of new service features have been provided by an Advanced Intelligent Network (AIN). In an AIN type system, central offices send and receive data messages from an Integrated Services Control Point (ISCP) via a Switching Transfer Point (STP). At least some calls are then controlled through multiple central office switches using data retrieved from a database in the ISCP. Some attempts have been made to provide Centrex or closely related private virtual network services using AIN type architectures.
An Area Wide Centrex service using an AIN type network implementation was proposed in commonly assigned U.S. Pat. No. 5,247,571. With the system disclosed in that application, a number of the local communication lines connected to each central office switching system are designated as members of a business group for a particular customer. For each requested service feature, including extension number dialing, one of the central offices accesses a database in the integrated services control point (ISCP). Establishing or changing services for one or all of a particular customer's lines requires only reprogramming that customer's data in the central database, without the need to reprogram each central office switch. Also, Centrex services such as extension number type intercom dialing and call transfer, which could be provided only between lines connected to the same exchange were extended across exchanges.
The prior patent teaches accessing the database using a dialed extension number which consists of fewer than the minimum number of digits required for a complete telephone number. This facilitates extension number dialing using three, four or five digits, rather than requiring seven or ten digit dialing. However, feature conflict problems arose with this approach. Specifically, switch vendors maintain that to avoid conflicts in call processing routines an Area Wide Centrex line which can have the short number extension dialing must not have any other features associated with that line in the connected end office switch. This means that the business customer can subscribe to Area Wide Centrex but cannot also subscribe to any switch provided features, such as call forwarding or call pickup.
A system providing private virtual network services, similar to the above discussed Area Wide Centrex Service was described in Pierce et al., "Meeting Private Needs with the Public Network," Bellcore Exchange, Jan/Feb 1988, pp. 8-13. The private virtual network system of Pierce et al. and other similar systems use at least a full seven digit number as the extension numbers because many existing switches are not programmed to initiate the query and response procedure with a central database using only short extension numbers. Such switches require dialing of complete seven or ten digit telephone numbers prior to initiating the database communication procedure. Many customers, however, want to be able to use shorter extension numbers in a manner similar to that provided by many PBX dialing plans.
From the above discussion, it should be clear that a need still exists to develop an AIN type system which can provide short number extension dialing and similar Centrex type services through multiple end offices without requiring the line to have no associated switch provided type services which may cause call processing conflicts and which will allow use of switch programs set up to process AIN type calls using a complete seven or ten digit dialed telephone number.